黔东南州下寒武统黑色页岩稀土元素地球化学特征

Geochemical characteristics of rare earth elements in Lower Cambrian black shale in Southeast Qian

采用等离子质谱仪（ICP-MS）对三穗和黄平下寒武统斜坡相黑色页岩稀土元素含量进行分析。结果表明：稀土总量为68.28×10-6~252.00×10-6,平均含量为133.16×10-6;ΣLREE/ΣHREE的比值是2.38~5.70,轻稀土元素较重稀土元素富集。δEu=0.49~0.75,推测沉积温度低于250℃;δCe=0.34~0.85,反映岩石是在相对缺氧的海水环境条件下沉积。岩石（La/Sm）N的比值是1.77~3.31,代表有地下深部物质加入。黑色页岩稀土的球粒陨石配分曲线为向右倾斜,而其北美页岩组合样标准化曲线明显呈近于水平或左倾。结合La/Ce和La/Yb-REE判别图解,推断黔东南州黑色页岩形成于一种干燥缺氧较深浅海环境,并在形成过程中有热液参与。

The abundances of rare earth elements（REE） of the black shale on the slope facies from Lower Cambrian in Sansui and Huangping were measured by using inductively coupled plasma mass spectrometry（ICP-MS）.The results show that the total REE content is 68.28×10-6-252.00×10-6,the average one is 133.16×10-6;the ratio of ΣLREE to ΣHREE is 2.38-5.70,which shows that LREE are relatively more intensive than HREE.δEu=0.49-0.75,which shows that the deposition temperature is below 250 ℃.δCe=0.34-0.85,which reflects that a rock deposits under the condition of relatively hypoxic sea.The ratio of rock（La/Sm）N is between 1.77 and 3.31,which represents that it has added with the materials from deep resource.The chondrite normalized patterns of black shale incline to the right,the North American shale normalized REE patterns of siliceous rocks are nearly flat or left.Combined with the discrimination diagrams of La/Ce and La/Yb-REE,the black shale of Southeast Qian formed in a dry,hypoxia and shallow sea,with the participation of some hydrothermal fluids in the formation process.